A. Field of the Invention
The present invention relates to an arc extinguishing resin processed article having flame retardancy used to extinguish an arc generated from contacts upon interruption of electric current of a circuit breaker or the like, and a circuit breaker using the same.
B. Description of the Related Art
In a circuit breaker or the like, when a contact point of a movable contact and a contact point of a fixed contact are opened when passing excess current or rated current, an arc is generated between the contact points. To extinguish this arc, an arc extinguishing apparatus equipped with an arc extinguishing chamber comprising an arc extinguishing member is generally provided around an arc generation part. The arc extinguishing member is pyrolyzed by the arc, and the arc is extinguished by a pyrolysis gas generated from the arc extinguishing member.
These arc extinguishing members mainly use thermosetting resins such as unsaturated polyester resins (see Japanese Patent No. 3098042) and melamine resins (see JP-A-2-256110), and thermoplastic resins such as polyolefin resins, polyamide resins and polyacetal resins (see JP-A-7-302535), as a matrix resin.
However, a thermosetting resin is liable to generate burrs when molded, and therefore has the problem that molding processability is poor as compared with a thermoplastic resin. Furthermore, a pyrolysis gas is generated from an arc extinguishing member upon the extinction of an arc, and therefore, an inner pressure in an arc extinguishing apparatus is increased. A thermosetting resin is relatively hard, but is liable to be broken and is poor in compression strength, and it was difficult in such a thermosetting resin to reduce a size of an arc extinguishing apparatus.
A thermoplastic resin does not tend to generate burrs when molded, but is poor in strength, pressure resistance and heat resistance, and an arc extinguishing member made with such resins have the tendency to deform or deteriorate with the passage of time. A thermoplastic resin having a large content of an aromatic ring, such as an aromatic polyamide resin, is excellent in strength, pressure resistance and heat resistance, but is liable to liberate free carbon upon burning. For this reason, where a thermoplastic resin having a large content of an aromatic ring is used, there is a possibility that an arc extinguishing apparatus is corroded with carbon, and there was a problem that insulating properties of the arc extinguishing apparatus are impaired.
To improve strength, pressure resistance, heat resistance and insulating properties of an arc extinguishing apparatus, attempts are made to add inorganic fillers such as reinforcing fibers or metal hydroxides to an insulating thermoplastic resin or thermosetting resin (see Japanese Patent No. 3098042, JP-A-2-256110, JP-A-7-302535, JP-A-8-171847 and WO98/36028). However, the amount of a pyrolysis gas generated tends to decrease with the increase in the content of inorganic fillers, and there is a problem that arc extinguishing properties are decreased.
On the other hand, JP-A-2003-31063 discloses a resin molded article for electrical insulation comprising microcapsules containing water as a core component, and inorganic fillers comprising alumina or aluminum hydroxide.
WO2003/044818 discloses a circuit breaker using a resin processed article obtained by applying electron beam treatment to a thermoplastic resin such as a polyester or a polyamide.
The molded article for electrical insulation disclosed in JP-A-2003-31063 comprises microcapsules containing water as a core component, and inorganic fillers comprising alumina or aluminum hydroxide. By this constitution, even where microcapsules are collapsed when the surface of a resin molded article is pyrolyzed upon the generation of an arc, so that inner water (water vapor) is released and free carbon is formed on the surface of a resin molded article, the free carbon is reacted with water in the presence of alumina as a catalyst to form carbon monoxide or hydrocarbon. Therefore, the amount of free carbon can be decreased, and it is possible that insulation properties of an arc extinguishing apparatus are difficult to be impaired. However, in JP-A-2003-31063, no investigation is made to attempt to suppress rise in inner pressure of an arc extinguishing apparatus by a pyrolysis gas generated upon the extinction of arc, and to attempt improving heat resistance and pressure resistance of an arc extinguishing apparatus.
WO2003/044818 improves strength, heat resistance and pressure resistance of a resin processed article by applying electron beam irradiation to a thermoplastic resin, but its effect was not sufficient. Specifically, permeation of electron beam may be insufficient in electron beam irradiation, and crosslinking might not be conducted uniformly. Furthermore, little or no improvement in arc extinguishing properties was recognized. Additionally, the rise in inner pressure of an arc extinguishing apparatus due to a pyrolysis gas generated upon the extinction of an arc cannot substantially be suppressed, and an arc extinguishing apparatus was liable to be broken due to the rise in inner pressure upon the extinction of an arc.
In recent years, the required level of flame retardancy required to a resin material used in a circuit breaker has increased. In improving flame retardancy, it is considered to use a flame retardant resin as a matrix resin in an arc extinguishing material. It is known that a halogen compound such as bromine is effective for the flame retardation of a resin, and resins with a halogen compound added are generally and widely used as a flame retardant resin. However, there was a possibility that a flame retardant resin containing a large amount of a halogen compound generates dioxins depending on combustion conditions.
The present invention is directed to overcoming or at least reducing the effects of one or more of the problems set forth above.